1. Field of the Invention:
The present invention relates to a passenger protection system for vehicles- More particularly, the present invention relates to a system for controlling and actuating an airbag system when the vehicle is in a collision and thereby protecting the passengers of the vehicle from injury.
2. Related Art:
Airbag systems that are intended to protect the passengers of motor vehicles from injury resulting from collisions. Such airbag systems must inflate promptly in a collision to protect the passengers from injury. For example, in the case of a driver side airbag, the airbag must be quickly inflated by gas that is charged via ignition of an ignition system located in the steering wheel or steering wheel shaft in front of the driver's seat. The shock of a collision is detected by a collision detecting system, which transmits a signal to the airbag ignition system, in turn causing ignition of the airbag. In this manner the driver is protected from injury. Such a system is also used with respect to passenger side airbags.
The ignition system receives power from a battery power source included in the vehicle. Should the ignition system be disconnected from the battery, which often occurs in a collision, normal operation of the ignition system is not assured nor is inflation of the airbag. Thus, the airbag system includes a supplementary power source such as a back-up condenser for storing electrical power. For power to be supplied to the airbag without fail at the time of a collision, charging power must be always available from the battery installed in the vehicle.
However, since the supplementary power source such as the back-up condenser is directly connected to the ignition system, when the power supply voltage of the power source drops, the energy accumulated in the supplementary power source is discharged. Fluctuation of the power supply voltage of the battery is unavoidable, and this causes continuous charging and discharging of the supplementary power source.
Even when the battery power source is experiencing a voltage drop and hence energy is being discharged from the supplementary power source, it is important to have available sufficient power to operate the airbag, i.e., inflate the airbag in the event of an accident. For this reason, the back-up condenser that constitutes the supplementary power source is required to have a large capacity. To compensate for the continuous dropping of the battery power supply voltage, it is also necessary to have a large-capacity step-up (booster) circuit. Such a large capacity circuit and condenser require excess space in the vehicle, thereby taking up space which could be occupied by other systems or be used for passenger space. Furthermore, the step-up circuit requires excess power to operate.